CB750 Barn find project - First Timer

[Underdog1]

Well the oil tank and battery tray fit with about 1mm clearance so happy with that! Had a go making a new seatpan up today by forming the 1.2mm steel sheet with a hammer, didn't go brilliantly as I think it's a bit thick.

Will just have to make it in sections and weld together

[Nurse Julie]

I will be interested to see how you get on with your seatpan as I'm just about to start making one for my CB550 custom. I haven't got a clue where to start!!

[Underdog1]

Finally got the seatpan figured out. I’ve been scratching my head over how I could get the clearance for the rear mudguard/rear wheel whilst still being able to securely mound the seatpan both front and back. After a few different ideas (some of which could have worked if I was better at metal forming/ had the right tooling) I decided to create a flat seatpan with a kick up to match the rear hoop, then remove a circle of metal where the mud guard needed clearance and weld on another section of metal to form a cavity. Seems to simple!

Ready to be welded up:


All done:



Not my neatest welding but it’s all going to be hidden away anyway.

Need to make a little bracket to mount my reg rec on the battery tray and it can all go get powder coated (pending not being skint that is).

I’m going to get my seat professional upholstered, but is it worth giving the foam work a bash myself? In my head I can just layer some close cell foam on top with glue and then carve into shape.

[Nurse Julie]

What metal and what thickness is the seat pan please?

[Underdog1]

What metal and what thickness is the seat pan please?

Its 1.2mm mild steel. Just looks shiny as it’s been wire brushed

[Nurse Julie]

What metal and what thickness is the seat pan please?

Its 1.2mm mild steel. Just looks shiny as it’s been wire brushed

Great, thanks. I know you are going to get it covered professionally but do you know how he is going to attach the cover to the base on the underside?

[Underdog1]

What metal and what thickness is the seat pan please?

Its 1.2mm mild steel. Just looks shiny as it’s been wire brushed

Great, thanks. I know you are going to get it covered professionally but do you know how he is going to attach the cover to the base on the underside?

I’d imagine either rivets orncover the whole thing like a sleeve. That’s upholsterer perks though 👍

[Laverda Dave]

Nice job Underdog, that's the fun of building a special, the working out of how to overcome problems and the satisfaction that comes with it when you do
I think you have mixed up an upholsterer with a Coach Trimmer though. An Upholsterer makes sofa's and dining room chairs, a Coach Trimmer make vehicle seats, carpets, headlinings, motorcycle seats etc.  I'm only saying this because I used to be a Coach Trimmer back in the day (wish I was still doing it, and still have all my tools and sewing machine in the loft!) 

[Underdog1]

Sorted out the mount for my solid state reg/rec

Cut the brackets for the old reg and rec off and decided I was going to mount it here


Put my ‘new’ bench drill to good use (it’s actually almost 70 years old!)



Welded some bolts through from the other side

And voila!


I can’t remember what this little bracket with a hole in is for so I left it on for now, any ideas?


Heard back from some automotive trimmer re getting my seat done.. £185

[Mag1]

Looking good this is. Nice work indeed

[Underdog1]

Picked up the tools today again.

Going to get all the bits to the powdercoaters tomorrow (if he's open), but i.m struggling getting the bushes for the shocks out the swingarm.





So one side i tried the ole threaded rod and socket trick to pull it out but the outer was stuck fast and remained in the swing arm. The other started going that way too so i tried to crimp the edges in a bit with a chisel but it won't budge.

Plan B is to cut it with a hacksaw and bash it out with something, any other methods worth trying first?


Stripped the wheels down today, managed to get the old tyres off in my garage with none of the correct tools.. wouldn't recommend it! Have ordered new spokes and cush drive bits to build them back up. Rims and hubs are going satin black, would like the spokes black too but they are expensive so have opted for a cheap stainless set from DS.

Still open to suggestions on where to get black spokes at a decent price as i can always cancel/ return the DS ones

[Deano400]

Used the hacksaw method on mine, two cuts. There is advice on here but I can't remember who posted it. With two close cuts removing a thin strip the rest came out easy.

[Underdog1]

Done a little research on how i can turn the spokes black, im reluctant to powder coat them loose as i think ill run into problems with them fitting through the hubs and flaking off around the threaded ends.

Best way seems to be gun blue which was developed to give steel a black oxide finish (originally on weapons hence the name). The spokes I've got are these from DS:

https://www.davidsilverspares.co.uk/CB750K6-FOUR-1976/part_105494/

Doesn't specify that they are zinc coated but i presume they are as surely they would advertise if they were stainless.. Plan is to use muriatic acid to remove the zinc coating and then use this:

https://www.amazon.co.uk/Birchwood-Casey-Liquid-Shotgun-Blueing/dp/B0091C0LBQ/ref=sr_1_4?s=sports&ie=UTF8&qid=1527504245&sr=1-4&keywords=gun+blue&dpID=41Qlxi9xPNL&preST=_SY300_QL70_&dpSrc=srch

Watched a few youtube videos and the process is simple. Probably the process which Central wheels uses to 'chemically blacken' their spokes that they sell for £100+

The muriatic acid shouldn't react with the steel beneath the zinc coating on the spokes so shouldn't weaken them at all. Will report back with results.

Edit: seems the black oxide only has limited rust protection, apparently the gun blue works on zinc alloys so might work with the coating left on. Other option would be to coat them with boiled linseed oil

[Trigger]

Take the spokes to a platter and have them black zinked 

[Underdog1]

Take the spokes to a platter and have them black zinked 

admittedly this would be a lot easier but presumably more costly? Ill look into it any way